To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, manufacturing of microelectronic devices at the 65-nm node by the ArF lithography has been implemented in a mass scale. Manufacturing of 45-nm node devices by the next generation ArF immersion lithography is approaching to the verge of high-volume application. The candidates for the next generation 32-nm node include ultra-high NA lens immersion lithography using a liquid having a higher refractive index than water in combination with a high refractive index lens and a high refractive index resist film, EUV lithography of 13.5 nm wavelength, and double patterning version of the ArF lithography, on which active research efforts have been made.
The current technology is approaching to the processing size which is reduced below 50 nm as minimum line width. When the processing size is so reduced, the thickness of resist film must be reduced below 100 nm, depending on the surface material of the substrate to be processed, because of such factors as the structural strength to maintain the pattern against the surface tension of developer and the adhesion strength to the substrate. On use of prior art chemically amplified resist materials intended to form high-resolution resist film, for example, no significant degradation of line edge roughness (LER) does occur with a resist film having a thickness of 150 nm, but LER is materially exacerbated when the film thickness is reduced below 100 nm.
As the feature size is reduced, image blurs due to acid diffusion become a problem (see Non-Patent Document 1). To insure resolution for fine patterns with a size of 45 nm et seq., not only an improvement in dissolution contrast as intended in the prior art is requisite, but control of acid diffusion is also important. Since chemically amplified resist compositions are designed such that sensitivity and contrast are enhanced by acid diffusion, an attempt to minimize acid diffusion by reducing the temperature and/or time of post-exposure bake (PEB) results in drastic reductions of sensitivity and contrast.
Addition of an acid generator capable of generating a bulky acid is effective for suppressing acid diffusion. It is then proposed to copolymerize a polymer with an acid generator in the form of an onium salt having polymerizable olefin.
With respect to the patterning of a resist film to a feature size of 16 nm et seq., it is believed impossible in the light of acid diffusion to form such a pattern from a chemically amplified resist film. It would be desirable to have a non-chemically amplified resist material.
A typical non-chemically amplified resist material is polymethyl methacrylate (PMMA). It is a positive resist material which increases solubility in organic solvent developer through the mechanism that the molecular weight decreases as a result of scission of the main chain upon exposure to EB or EUV. Due to the lack of cyclic structure, it has the drawbacks of poor etch resistance and substantial outgassing during exposure.
Hydrogensilsesquioxane (HSQ) is a negative resist material which turns insoluble in alkaline developer through crosslinking by condensation reaction of silanol generated upon exposure to EB or EUV. Also chlorine-substituted calixarene functions as negative resist material. Since these negative resist materials have a small molecular size prior to crosslinking and are free of blur by acid diffusion, they exhibit reduced edge roughness and very high resolution. They are thus used as a pattern transfer material for representing the resolution limit of the exposure tool. However, their sensitivity is two orders of magnitude lower than that of chemically amplified resist materials.
There is a demand for a non-chemically amplified molecular resist material having a sensitivity equivalent to chemically amplified resist materials and a high resolution.
The EB writing of a resist film encounters a problem that the point of writing is shifted by electrostatic charges on the resist film. It is proposed to overlay the resist film with an antistatic film to prevent the resist film from being charged. Undesirably coating of the antistatic film adds to the cost of the overall process.
It was impossible to use metal-containing materials as the photoresist material for the semiconductor lithography because of a possible malfunction of semiconductor devices as a result of metal atoms migrating to the substrate. However, it is known in the application other than the semiconductor, for example, to use a metal compound as the resist material for LCD (see Non-Patent Document 2) or zinc neodecanoate as the patterning material for forming transparent electrode of ZnO. Patent Document 1 shows pattern-forming examples using complexes of silicon, titanium, zirconium, tantalum, barium, strontium, and hafnium with acetylacetone ligands. Patent Document 2 discloses a method for forming a pattern using salts of copper, chromium, cerium, yttrium, barium, and aluminum with carboxyl and amino-containing ligands. Once a pattern is formed, it is converted into a pattern of metal oxide by heat treatment at 300° C.
In the cited documents, a film of metal resist material is formed by spin coating. To enable spin coating, the resist material is diluted with solvents, for example, chloroform, methylene chloride, toluene, acetone, dimethyl sulfoxide, dimethylacetamide, and 2-methoxyethanol. These solvents, however, cannot be used in the industrial application because of their toxicity. In addition, these solvents having low boiling points have so high evaporation rates during spin coating that they may dry up during film formation before the coating thickness becomes uniform. The lack of coating thickness uniformity is a problem.
In the cited documents, development uses resist solvents, which also suffer from the toxic problem.